Alkali free lead silicate glass medium for ultrasonic delay lines

ABSTRACT

A glass medium suitable for ultrasonic delay lines employs a composition which consists essentially of 36 to 46 percent of SiO2, 35 to 60 percent of PbO, 0 to 20 percent of AlF3 and 0 to 10 percent of BaF2, the total content of the AlF3 and BaF2 being present in a range of 2 to 20 percent, the percentage being by weight.

United States Patent [191 Inamura et al.

[451 Dec.31, 1974 ALKALI FREE LEAD SILICATE GLASS MEDIUM FOR ULTRASONICDELAY LINES Inventors: Takahiro Inamura; Kenichi Sawamoto; NobukazuNiizeki, all of Laboratory of Nippon Telegraphy & Telephone PublicCorporation,

9-1 1, 3-chome, Midori-cho; Munehisa Tsunekawa; Yasuyuki Nakata, both ofOhi Kojyo of Nippon Kogaku K.K., 63, l-chome, Nishi-Ohi, all of Tokyo,Japan Filed: June 19, 1972 Appl. No.: 264,338

Related U.S. Application Data Continuation-impart of Ser. No. 63,194,Aug. 11, 1970, abandoned.

U.S. Cl. 106/53 Int. Cl. C03c 3/10, C03c 3/30, C030 3/04 Field of Search106/53 Primary E.raminerWinston A. Douglas Assistant Examiner-Mark BellAttorney, Agent, or Firm-Shapiro and Shapiro [5 7] ABSTRACT A glassmedium suitable for ultrasonic delay lines employs a composition whichconsists essentially of 36 to 46 percent of SiO 35 to 60 percent of PhD,0 to 20 percent of AlF and 0 to 10 percent of BaF the total content of.the A11 and BaF being present in a range of 2 to 20 percent, thepercentage being by weight.

4 Claims, 4 Drawing Figures mmwnm 3.857. 113 SHEET 10? 2 FIG. 3'

||II I ILIIIIII 1 I llIIlll I I0 I00 AGING (DAY) FIG. 4

RATE OF VARIATION -1IL OF DELAY TIME EXAMPLE 3 EXAMPLE I RATE OFVARIATION OF DELAY TIME I 1 I l TEMPERATURE (C) ALKALI FREE LEADSILICATE GLASS MEDIUM FOR ULTRASONIC DELAY LINES This application is acontinuation-in-part of our pending application Ser. No. 63,194; filedAug. 11, 1970, now abandoned.

FIELD OF INVENTION The present invention relates to a glass medium forultrasonic delay lines having improved acoustic properties.

BACKGROUND OF INVENTION In general, an ultrasonic delay line consists ofa medium through which acoustic waves are propagated, an inputtransducer fixed to a suitable portion of the medium for convertingelectrical signals into mechanical signals and an output transducer forconverting the mechanical signals again into electrical signals.

The most important factors of a medium used as a delay line are that thedelay time will not be varied by temperature variation, that theattenuation of the propagated acoustic wave be minimal, and that theaging also be minimal. Glasses as ultrasonic media are required to meetsevere conditions for such special uses. For example, when a glass isused as a delay line in a PAL color television receiver, the variationin delay time together with the aging must be within :80 ppm. Theattentuation is preferred to be less than X 10 db/ cycle when measuredwith a frequency higher than 1 MHZ. A fused silica which has been usedwidely as a delay line has a temperature coefficient (a ratio ofvariation of delay time to a temperature rise of 1C) of In summary, thenovel features which are believed to characterize the present inventionreside in the facts that the glass compositions of the present inventionpossess every property to satisfy the conditions required as a delayline and that the production of the glass is much facilitated.

BRIEF EXPLANATION OF THE DRAWING FIG. 1 is a schematic illustration of abar-shaped ultrasonic delay line;

FIG. 2 is a graph illustrating the composition of a glass in accordancewith the present invention;

FIG. 3 is a graph illustrating rate of variation of delay time due toaging; and

FIG. 4 is a graph illustrating the rate of variation of delay time dueto temperature variation.

PREFERRED EMBODIMENTS OF THE INVENTION The invention may be understoodwith reference to FIG. 1, which shows a common and simple form of delayline consisting of a delay line medium 2 in the form of a bar and inputand output transducers l and 3 fixed to the ends thereof. The shearwaves of the me chanical signals converted by the input transducer 1propagate through the medium 2 and are converted again into theelectrical signals by the output transducer 3. The delay time is thetime for the acoustic wave to propagate through the medium 2 between theinput and output transducers land 3.

FIG. 2 is a graph illustrating the composition range of a glasscomposition in accordance with the present invention. The glass consistsof 36 46 percent by Hal",

about 80ppm/C. The glasses available on the market weight of Stow 35 60percent by weight of Pbo, 0 have a temperature coefficient from 10 ppm/Cto 50 20 percent by weight of AiFa and 0 10 percent by C and agmg 100 F.to 1000 weight of BaF The total content of the AIF and Ba] whichdepending upon their compositions represent a is present in the range of2 to 20 percent by weight. wide variation. Conventional glasses do notpossess the when th6 fluoride content is Smaller than th aboveproperties to permit their satisfactory use as delay lines. mentionedrange, the viscosity of the fused glass iS 7 creased, and unresolved SiOtends to remain so that it is difficult to attain a high degree ofhomogenization. SUMMARY OF I NT It is therefore preferable that thefluoride content be higher than 2 percent by weight. From the standpointIt therefore. the pnmary f of the present of stability, the fluoridecontent is preferably less than vention to provide a glass compositionto be used as a 20 percent by weight The contents of Pbo and sioz mwhich el'minate.s.the defects .encoumered are somewhat differentdepending upon the contents with prior art glass compositions, and whichpossesses and types of fluorides, but a glass having a temperaturesatisfactory properties as a delay line. The temperature coefficient inthe range of to +5ppm/oC may be coefficient is in the range of 5 to +5ppm/0C the tained by the contents of 36 46 percent by weight oftenuafio'n is less than 10 X 10-3 lb/cycle h F SiO and 35 60 percent byweight of PhD. The attenu- Sured 3 frequency of 5 agmg ation of theglass of the invention is less than 10 X l0 most zero. Another advantageresides in the fact that db/cycie when measured with a frequency higherthan glass compositions in accordance with the present in- 1 MHZ and theaging of deiay time iS less than 50 ppm vention may be Produced in aconsiderablytshorter by an accelerated aging test in' which the glass issubnealing time as compared to the time required to proiected to aStrain of 10-6 at with an aitematiiig duce prior art delay line glass.As a result, aging is minicurrent f 1 m ZBd- Since the glass of thisinvention contains a lead oxide,

Furthermore, the Viscosity and the melting p the velocity of shear wavemay be small so that the diture of molten glass made in accordance withthe inmensions of the glass may be made smaller compared vention arelower because the glass contains fluorides, ith th prior n l ss, wherebymelting and forming of the glass are greatly The table below shows thecompositions, of the Ex facilitated. amples and their acousticcharacteristics:

Examples 1 2 3 4 5 6 7 8 9 sio by wt.) 40.0 40.0 40.3 421 g) gals) 13.332. 25. 2?, 2:8 2:2 3215 1 05 10:5 gig it i Table Continued Examples 1 23 4 pp 0C 50C Velocity km/sec.

The attenuation of each of the Examples was less than prepared by thefollowing process. A glass batch (total 10 X 10 db/cycle and the agingin years was less than 50 ppm as shown in FIG. 3. The temperaturevariations for Examples 1 and 3 are shown in FIG. 4. Aging tests weremade at 50C under a continuous strain of 10 by an alternating current ofSMHz. The density of each glass was about 4g/cm In the production ofprior art glasses for delay lines, fine control of temperature and timeare required. In accordance with the present invention control oftemperature and time are not critical and the acoustic properties of theglass of the present invention will not vary though the control ofconditions of temperature and time may vary. For example, in case ofExample 1 consisting of 40.0 percent by weight of SiO 56.0 percent byweight of PbO and 4.0 percent by weight of AlF the temperaturecoefficient, attenuation and aging remained almost unchanged even whenthe annealing temperature was changed from 1C/Hr. to 30C/Hr., with adecrease in velocity of only 0.5 percent. The viscosity of the moltenglass of the invention is reduced because the glass contains fluorides.For example, the melting temperature of the glass of the invention islower by 50 150C than the melting temperature of the prior art glasscontaining only oxides. Thus the glass melting conditions are muchimproved.

The raw materials of the glass in accordance with the present inventionmay be mixed in the conventional manner and melted in a clay pot orplatinum crucible at a temperature from 1,200 to 1,350C. The fused glassmay be formed by the conventional method. The continuous flow or tankfurance method may, of course, be employed. When a refining agent suchas Sb O A5 0 etc., is added to the raw materials in a very smallquantity, the homogenization of the glass may be much improved.

For example, glass in accordance with Example 1 is amount about 200.0kg) comprising 80.0 kg of SiO 108.74 kg of PbO, 8.1 kg of AIR, and 1.0kg of Sb O is well mixed by a known method, and the mixture is heated at1,350C for 5 hours in a clay crucible. The molten glass is stirred for15 minutes under 40 revolutions per minute. Then the molten mixture iscooled to a temperature suitable for casting. The cooled, molten glassis thrown in a cast, and annealed to room temperature at an annealingrate 1.5C/hr.

Glass made in accordance with the present invention has satisfactoryproperties for ultrasonic delay lines and may be produced in a simplemanner.

We claim:

1. A glass medium for ultrasonic line having the range of 5 to +5 ppm/Cof the temperature coefficient of delay time, attenuation of less thanapproximately 10 X 10' db/cycle at a frequency higher than 1 MH andaging of delay time ofless than 50 ppm, the glass medium being devoid ofan alkali ion and consisting essentially of, by weight, 36 to 46 percentof SiO 35 to 60 percent of PbO, 0 to 20 percent of AlF and O 10 percentof BaF the total content of the AlF and BaF being present in a range of2 to 20 percent.

2. A glass medium according to claim 1 wherein the SiO is in the amountof 40.0 percent, the PbO is in the amount of 56.0 percent, and thefluoride is All], in the amount of 4.0 percent.

3. A glass medium according to claim 1, wherein the SiO is in the amountof 40.0 percent, the PbO is in the amount of 53.5 percent, and thefluoride is AlF in the amount of 6.5 percent.

4. A glass medium according to claim 1 wherein the SiO is in the amountof 41.0 percent, the PhD is in the amount of 50.5 percent, and thefluoride is BaF in the amount of 8.5 percent.

1. A GLASS MEDIUM FOR ULTRASONIC LINE HAVING THE RANGE OF -5 TO +5PPM/*C OF THE TEMPRATURE COEFFICIENT OF THE TEMPERATURE COE ATTENUATIONOF LESS THAN APPROXIMATELY 10X10**-3 DB/CYCLE AT A FREQUENCY HIGHER THAN1 MH2, AND AGING OF DELAY TIME OF LESS THAN 50 PPM, THE GLASS MEDIUMBEING DEVOID OF AN ALKALI ION AND CONSISTING ESSENTIALLY OF, BY WEIGHT,36 TO 46 PERCENT OF SIO2, 35 TO 60 PERCENT OF PBO, 0 TO 20 PERCENT OFALF3 AND 0 -10 PERCENT OF BAF2, THE TOTAL CONTENT OF THE ALF3 AND BAF2BEING PERSENT IN A RANGE OF 2 TO 20 PERCENT
 2. A glass medium accordingto claim 1 wherein the SiO2 is in the amount of 40.0 percent, the PbO isin the amount of 56.0 pErcent, and the fluoride is AlF3 in the amount of4.0 percent.
 3. A glass medium according to claim 1, wherein the SiO2 isin the amount of 40.0 percent, the PbO is in the amount of 53.5 percent,and the fluoride is AlF3 in the amount of 6.5 percent.
 4. A glass mediumaccording to claim 1 wherein the SiO2 is in the amount of 41.0 percent,the PbO is in the amount of 50.5 percent, and the fluoride is BaF2 inthe amount of 8.5 percent.